The USPSTF, a panel of independent medical experts, said it was recommending against annual mammograms for women between the ages of 40 and 49, saying the risks outweighed the benefits from earlier screening. That announcement, which goes against a trend of recommending increased screening by cancer agencies, has left many confused.

Meanwhile, doctors' offices and hospitals have been fielding calls from women wanting to know what these new guidelines will mean for them.

One of these calls came not from a woman concerned about getting breast cancer but one who has already had it. Beth Thompson, 44, a mother of four who lives in the suburbs of Baltimore, Md., was first diagnosed with breast cancer following a mammogram at the age of 40.

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"I had no risk factors and no family history," Thompson told ABCNews.com. "Under the new guidelines I wouldn't be screened. That's why I'm so upset about this. I firmly believe I would not be here today if I had not had a screening mammogram at 40."

Thompson explained that in removing the tumor detected by the mammogram, doctors found a faster-growing one underneath, one that would not have been found until it became a palpable lump.

"It really makes me shudder to think of what a different situation I would have been in if that were the case," she said, explaining that she needed four surgeries, four rounds of chemotherapy and took Herceptin, an adjuvant for an aggressive form of breast cancer, for a year.

"That's the treatment that I needed even for an early-stage cancer," Thompson said. "There's just no reason that I would have been screened and no way that it would have been found at the time, except for mammography."

According to most medical centers that ABC News has heard from, the new screening guidelines will not be followed. M.D. Anderson, the Mayo Clinic, Baylor College of Medicine and Fox Chase Cancer Center were among many hospitals that said they are sticking with the current guidelines, recommended by the American Cancer Society.

"[Some] women don't understand how screening can cause problems," said Dr. Bob Crittenden, an associate professor in family medicine at the University of Washington. "Personally, I think this is symptomatic of many in people in medicine promising good health if you get screened. As we know with PSAs and other screenings of asymptomatic people, we have only a few things we can do that actually help extend life and then usually only marginally."